Question

(i) Indicate the principle behind the method used for the refining of zinc.
(ii) What is the role of silica in the extraction of copper?
(iii) Which form of the iron is the purest form of commercial iron?

Answer 1

Zinc is refined using electrolytic refining process. During electrolytic refining, pure zinc metal transports from anode to cathode. Silicon dioxide is used to remove the impurity formed during the oxidation of copper ore.

Complete step-by-step answer:
i) The refining of zinc is done using electrolytic refining process. In the process of electrolytic refining, pure zinc metal is transported from the impure sample at anode to cathode. The metal which is more basic remains in the electrolytic solution while the less basic metal present as impurity precipitates out as anode mud.

The reactions occurring at anode and cathode are as follows:
Anode: ${\text{Zn}} \to {\text{Z}}{{\text{n}}^{2 + }} + 2{{\text{e}}^ - }$ (From anode)
Cathode: ${\text{Z}}{{\text{n}}^{2 + }} + 2{{\text{e}}^ - } \to {\text{Zn}}$ (From electrolyte)

ii) The most common ore of copper is copper matte. Copper matte contains copper sulphide along with small amounts of iron sulphide. The amount of copper sulphide is ${\text{80 - 95\% }}$ and the remaining amount is iron sulphide.

The extraction of copper from copper matte is done in a blast furnace. During the extraction, copper matte is added to the blast furnace along with powdered coke and silicon dioxide.
The oxidation of copper matte occurs in the blast furnace and as a result cuprous oxide and iron oxide are produced.

The role of silica in the form of silicon dioxide is to remove the ferrous oxide by combining with it. Iron oxide combines with silicon dioxide and forms iron silicate. The reaction of iron oxide with silicon dioxide is as follows:
${\text{FeO + Si}}{{\text{O}}_2}{\text{ }}\xrightarrow{{{\Delta }}}{\text{ FeSi}}{{\text{O}}_2}$
The iron silicate $\left( {{\text{FeSi}}{{\text{O}}_2}} \right)$ formed in the reaction is known as slag.

iii) The purest form of commercial iron is wrought iron. Wrought iron contains only $0.12 - 0.25\%$ carbon and the remaining is iron. Thus, wrought iron is the purest form of commercial iron.

Note: The most common ores of zinc are calamine or smithsonite. In these ores, zinc is found in the form of zinc carbonate $\left( {{\text{ZnC}}{{\text{O}}_{\text{3}}}} \right)$. The most common ore of copper is copper matte. Other forms of iron are pig iron, cast iron and steel.